Collective Phenomena in Strongly Coupled Dissipative Systems of Charged Dust: from Ground to Microgravity Experiments

In present work the formation of dusty plasma structures in cryogenic glow dc discharge was investigated. The ordered structures from large number (～10⁴) of charged diamagnetic dust particles in a cusp magnetic trap have been also studied in microgravity conditions. The super high charging (up to 5·10⁷e) of dust macroparticles under direct stimulation by an electron beam is experimentally performed and investigated. The results of the investigation of Brownian motion for strongly coupled dust particles in plasma are presented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-self-sustained discharge in nitrogen with a condensed dispersed phase

A non-self-sustained discharge in nitrogen with a condensed dispersed phase is studied experimentally for the first time under atmospheric pressure at room temperature. It is shown that macroparticles strongly affect the current-voltage characteristics as well as the stability of the discharge process. A numerical simulation of dust particle charging in nitrogen is carried out at room temperature and cryogenic temperatures under continuous medium conditions. It is shown that a considerable charge is accumulated at macroparticles in the nitrogen beam plasma. As the gas temperature decreases, the charge of macroparticles in nitrogen increases, while in argon their charge decreases. For this reason, the Coulomb interaction parameter for dust particles in nitrogen increases strongly upon a transition from room to cryogenic temperature, while in argon this parameter decreases. It is also shown that the characteristic time of dust particle charging is shorter than 1 μs for a beam current density of 90 μA/cm², while the neutralization of the charge takes milliseconds. Possible mechanisms of the influence of the dust component on the characteristics of non-self-sustained discharge are considered.     

Analysis of macroparticle charging in the near-electrode layer of a high-frequency capacitive discharge

Spatial variation of dust particle charges are estimated numerically for typical laboratory experiment conditions in a radio-frequency (rf) capacitive discharge. The surface potentials of macroparticles levitating in the upper part of the near-electrode layer of the rf discharge are measured. A model is proposed for the formation of irregular dust oscillations due to stochastic motion of dust in the bulk of a spatially inhomogeneous plasma (in the presence of a dust charge gradient). This mechanism is used for analyzing the results of measurements of the amplitude of vertical vibrations of dust particles in the near-electrode layer of the rf discharge. It is found that the dust charge gradient may be responsible for the development of such vibrations.     

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al₂O₃, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles. Zh. éksp. Teor. Fiz. 112, 2030–2044 (December 1997)     

Ultrahigh charging of dust particles in a nonequilibrium plasma

Charging of dust particles in a plasma with the two-temperature energy distribution of electrons has been studied. It has been shown that the dust-particle potential divided by the electron temperature decreases with increasing electron temperature in the plasma with cold ions. Owing to this behavior, the potential of the dustparticle surface increases with the electron temperature more slowly than the linear function and is lower than the electron temperature (divided by the elementary charge) for T _e > 5.5 eV in hydrogen and for T _e > 240 eV in argon. The fraction of fast electrons at which these electrons begin to contribute to the charge of dust particles has been determined. It has been shown that the charge of micron particles can reach 10⁶ elementary charges. The effect of the cold and thermal field emission on the charge of dust particles has been analyzed. The possibility of obtaining ultrahigh charges (to 10⁷ elementary charges on dust particles with a radius of 50–100 μm irradiated by a 25-keV 1-mA electron beam has been demonstrated.     

Effect of dust particles on the properties of low-temperature plasmas

Parameters of a low-temperature plasma containing dust particles are calculated numerically with the help of a self-consistent solution of the balance equation for production and recombination of electrons and ions, combined with the molecular dynamics method for direct simulation of processes in the vicinity of macroparticles. The relation between the charges of macroparticles and the neutral gas pressure, as well as the dependence of the low-temperature plasma parameters on the volume concentration of dust particles, is analyzed. It is shown that the plasma characteristics and composition may change noticeably relative to the case unperturbed by dust even for comparatively low concentration of dust particles.     

Anomalous heating of a system of dust particles in a gas-discharge plasma

The coexistence of regions of negatively charged macroparticles with substantially different kinetic temperatures in a highly nonideal dusty plasma in a dc glow discharge has been observed experimentally. An explanation of the observed anomalous heating of the system of dust particles in a gas-discharge plasma is proposed on the basis of a molecular-dynamics model. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 392–397 (25 September 1997)     

Dusty photoresonant plasma with coulomb collisions

We have studied the charging of dust particles in a dense photoresonant sodium plasma with electron and ion densities as high as 10¹⁶ cm^?3 produced by laser pumping of the resonance level of Na, which was a small admixture (up to 1%) in an argon buffer gas. We show that the charge of dust particles with a radius of 10 mm at maximum reaches 3 × 10⁵ electron charges and that the potential of the dust particles at a low electron bulk loss rate agrees well with the orbital motion limited (OML) model data. The behavior of the electric field near a dust particle was found to be nonmonotonic. We established that the distribution of the potential near a solitary charged dust particle agrees well with the Debye one, but the screening length proves to be much larger than even the electron Debye length; the discrepancies are largest at the afterglow stage of the photoresonant plasma, when the sodium ion with a low recombination coefficient is the main plasma ion. We determined the domain of parameters for a dense plasma where an ensemble of dust particles can crystallize.     

The diffusion of macroparticles and criteria of phase transitions for dust structures in weakly ionized plasma

The dynamics of charged particles is investigated under conditions close to those of experiments in a weakly ionized laboratory gas-discharge dust plasma. The existing phenomenological criteria of phase transitions for dust structures in such a plasma are treated, and new criteria are suggested. The parameters responsible for the order and scaling of dynamic processes in Yukawa dissipative systems are determined. The relation for the diffusion coefficient D of macroparticles in strongly correlated liquid structures is derived.     

Study of the magnetomechanical effect in a gas discharge with the use of dust particles

This paper reports on a test using laser Doppler anemometry of the hypothesis that the magnetomechanical effect involves rotation of the plasma of the positive gas-discharge column in an axial magnetic field. This was done by measuring the velocities of the dust macroparticles dropping in a vertical discharge tube. No rotation of the gas was revealed at a sensitivity of 40 cm/s. The rotation of dust particles suspended in striations and in the trap near the narrowed region of the discharge in a magnetic field was observed. The possible connection of this rotation with the magnetomechanical effect is discussed.     

Interaction of two macroparticles in a nonequilibrium plasma

The interaction of two macroparticles in a nonequilibrium plasma at elevated pressures has been investigated. An asymptotic theory of screening, which leads to a two-exponential dependence of the macroparticle potential on distance with different screening constants, is used to determine the electrostatic energy of the system of charges associated with the two macroparticles. The dependence of the electrostatic energy on interparticle distance has been found to have a minimum, as in an equilibrium plasma. The interaction force between the macroparticles has been determined; it turned out to be asymmetric—for different charges, the forces acting on the first and second macroparticles are not equal. This is the result of an asymmetric charge separation near macroparticles with differing charges and indicates that the interaction force in a nonequilibrium plasma is nonpotential. The forces are equal for identical macroparticles or in an equilibrium plasma and the potential energy of the interaction between the macroparticles has been determined for these cases. Attraction between likely charged particles with different (in magnitude) charges has been found to be possible when they come very close together. Relations to determine the modified coupling parameter for an interaction potential that consists of two exponential terms with different screening constants have been derived.     

Monitoring of pathogen carrying air-borne tea dust particles by light scattering

In order to investigate whether tea (Camellia sinensis (L.) Kuntze) dust particles could be a possible carrier of the pathogen contaminated Mycobacterium a biotechnical procedure was used, and to verify the possibility of monitoring this dust, a laser based light scattering setup was designed and fabricated. Experiments were carried out using the strain Mycobacterium smegmatis mc² 155 as a model organism to study the effect on tea dust particles. Light scattering investigations on both M. smegmatis contaminated and uncontaminated tea dust particle samples were carried out as a function of scattering angle at 543.5, 594.5 and 632.5 nm wavelengths. The results have shown that the behavior of tea dust samples both with and without Mycobacterium varies significantly for all the three different incident laser wavelengths.     

Dusty plasma induced by solar radiation under microgravitational conditions: An experiment on board the Mir orbiting space station

The dynamics of the formation of ordered structures of macroparticles charged by photoemission under the action of solar radiation under microgravitational conditions without the use of electrostatic traps to confine the particles is studied experimentally and theoretically. The working conditions needed for the formation of structures of charged macroparticles are chosen as a result of a numerical solution of the problem posed, the particle charges and the interparticle interaction parameter are determined, and the characteristic times specifying the dynamics of the formation of an ordered system of macroparticles are calculated. The behavior of an ensemble of macroparticles under the effect of solar radiation is observed experimentally on board the Mir space station. An analysis and comparison of the results of the experimental and theoretical investigations permit drawing a conclusion regarding the possibility of the existences of extended ordered formations of macroparticles charged by photoemission under microgravitational conditions. Zh. éksp. Teor. Fiz. 114, 2004–2021 (December 1998)     

Influence of inhomogeneous conditions on the kinetic energy of dust macroparticles in plasma

A brief review of the mechanisms leading to the “anomalous heating” of charged dust particles (macroparticles) in a plasma is presented. Their comparative characteristics are given. An analytical model to estimate the influence of spatial inhomogeneities on the anomalous heating of macroparticles in plasma–dust systems is proposed.     

Effect of thermophoretic forces on the formation of ordered structures of macroparticles in a thermal plasma

The thermophoretic interaction of macroparticles and its effect on the formation of ordered structures of macroparticles in plasma was studied. It was shown that coexistence of regions with a chaotic arrangement of particles and regions of ordered structures is typical of a thermal plasma with strong interaction of the macroparticles. Computer simulation of a system of strongly interacting macroparticles, taking account of the thermophoretic interaction of the particles, was performed. The results showed that the thermophoretic attractive forces explain the form of the spatial nonuniformity associated with the grouping of particles in small domains. The experimentally obtained correlation function was very close to the correlation function obtained in the computer simulation. Zh. éksp. Teor. Fiz. 116, 1601–1615 (November 1999)     

Laser-Induced Phase Transition in a Monolayer of Polymer Particles Levitating in a Low-Pressure Gas-Discharge Plasma

We report on the results of analysis of the mean kinetic energy and the pair correlation function of polymer particles in a plasma–dust structure under the action of laser radiation. We have observed experimentally the crystal–liquid phase transition in the monolayer of particles levitating in the near-electrode layer of a capacitive high-frequency discharge. The coupling parameter of the dust system has been estimated. The results of analysis of the modification of the polymer dust particle surface after holding in the plasma are considered. We propose an explanation of the phase transition taking into account the role of the photophoretic force in the motion of macroparticles. The effect of the photophoretic force is associated with the modification of the dust particle surface in the plasma, as a result of which the particles can effectively absorb laser radiation.     

Coulomb structures of charged macroparticles in static magnetic traps at cryogenic temperatures

Electrically charged (up to 10⁷ e) macroscopic superconducting particles with sizes in the micrometer range confined in a static magnetic trap in liquid nitrogen and in nitrogen vapor at temperatures of 77–91 K are observed experimentally. The macroparticles with sizes up to 60 μm levitate in a nonuniform static magnetic field B ~ 2500 G. The formation of strongly correlated structures comprising as many as ~10³ particles is reported. The average particle distance in these structures amounts to 475 μm. The coupling parameter and the Lindemann parameter of these structures are estimated to be ~10⁷ and ~0.03, respectively, which is characteristic of strongly correlated crystalline or glasslike structures.     

Dynamics of Macroparticles in a Quasi-Two-Dimensional Dust–Plasma System under Directed External Action: Simulation Results

The action of the light pressure force on a bounded region of a 2D system of dust macroparticles is simulated using the molecular dynamics method. The dynamics of dust macroparticles in the quasi-2D structure (trajectories of particles, their mean square displacement, and kinetic energy) is analyzed for various values of the nonideality parameter and laser radiation power. It is shown that by varying the radiation power, it is possible to influence the self-diffusion processes and the value of chaotic velocity of particles. Analysis is performed for different initial values of the nonideality parameter of the unperturbed dust subsystem. It is found that the interparticle interaction results in an increase in the kinetic energy of particles in the region of action, as well as beyond it.     

Charge and structures of dust particles in a gas discharge at cryogenic temperatures

A dusty plasma in a dc gas discharge is considered at low (cryogenic) temperatures of the gas. The formation of dusty plasma structures consisting of monodisperse poly(styrene) particles (d = 5.44 μm) in a dc glow discharge is experimentally investigated at cryogenic temperatures in the range from 4.2 to 77 K, and the results obtained are presented. The ion velocity distribution function and the charging of dust particles at cryogenic temperatures are calculated using the molecular dynamics method. The primary attention is focused on the correct inclusion of ion-atom collisions in the analysis. This is essential to the understanding of the main mechanisms of the experimentally observed increase in the density of dust particles with decreasing temperature of the gas in the discharge.     

Impacts of fast meteoroids and a plasma–dust cloud over the lunar surface

The possibility of the formation of a plasma–dust cloud in the exosphere of the Moon owing to impacts of meteoroids on the lunar surface is discussed. Attention is focused on dust particles at large altitudes of ~10–100 km at which measurements were performed within the NASA LADEE mission. It has been shown that a melted material ejected from the lunar surface owing to the impacts of meteoroids plays an important role in the formation of the plasma–dust cloud. Drops of the melted material acquire velocities in the range between the first and second cosmic velocities for the Moon and can undergo finite motion around it. Rising over the lunar surface, liquid drops are solidified and acquire electric charges, in particular, owing to their interaction with electrons and ions of the solar wind, as well as with solar radiation. It has been shown that the number density of dust particles in the plasma–dust cloud present in the exosphere of the Moon is ?10^?8 cm^?3, which is in agreement with the LADEE measurements.